fix(query): keep the trailing anchor when a zero-matched quantifier is anchored

on both sides

In `A . Q* . B`, a zero-matched `Q` made both anchors vacuous, so `A` and `B`
were no longer required to be immediate siblings. Only relax the following
anchor on a `?`/`*` zero-skip when the skipped step has no leading anchor of
its own; otherwise the adjacency transfers through the empty run.

crates/cli/src/tests/query_test.rs

@@ -1297,6 +1297,46 @@ fn test_query_matches_with_last_child_anchor_after_optional() {
     });
 }
 
+#[test]
+fn test_query_matches_with_anchors_on_both_sides_of_zero_quantifier() {
+    allocations::record(|| {
+        let language = get_language("javascript");
+        let query = Query::new(
+            &language,
+            "(program (lexical_declaration) @a . (comment)* . (function_declaration) @b)",
+        )
+        .unwrap();
+
+        // Anchors on both sides of a zero-matched quantifier collapse into a single
+        // adjacency constraint: with no comments, the declaration must be immediately
+        // followed by the function.
+        assert_query_matches(
+            &language,
+            &query,
+            "
+const a = 1;
+const b = 2;
+function foo() {}
+",
+            &[(0, vec![("a", "const b = 2;"), ("b", "function foo() {}")])],
+        );
+
+        // With a comment present the quantifier is non-zero, so the anchors apply
+        // normally: the comment must sit immediately between the declaration and the
+        // function.
+        assert_query_matches(
+            &language,
+            &query,
+            "
+const b = 2;
+// c
+function foo() {}
+",
+            &[(0, vec![("a", "const b = 2;"), ("b", "function foo() {}")])],
+        );
+    });
+}
+
 #[test]
 fn test_query_matches_with_last_named_child() {
     allocations::record(|| {

docs/src/using-parsers/queries/2-operators.md

@@ -239,6 +239,21 @@ nearest node that the pattern _does_ match. For example, given
 the trailing anchor requires the last matched node to be the parent's last named child: when a
 `preproc_else` is present it must be last. When it is absent, the last `preproc_def` must be last.
 
+Similarly, if an optionally quantified node is anchored between two siblings and matches zero nodes,
+both sibling anchors collapse into one, constraining the outer nodes together. For example, given
+
+```query
+(translation_unit
+  (declaration) @a
+  .
+  (comment)*
+  .
+  (function_definition) @b)
+```
+
+If there are no comments, `(declaration)` and `(function_definition)` must be immediate siblings
+in order for the query to match.
+
 An anchor may not appear at the first or last position inside a group `(...)` or an alternation
 `[...]`. A group or alternation is not a node, so it has no first or last child to anchor against,
 and there is no sibling on that side to anchor to. For example, write `(comment)* @doc . (function)`

lib/src/query.c

@@ -4478,8 +4478,12 @@ static inline bool ts_query_cursor__advance(
                   copy->seeking_immediate_match = true;
                 }
                 // Taking a `?`/`*` zero-skip means the quantified subpattern matched
-                // nothing, so an immediately-following anchor is vacuous for this copy.
-                if (child_step->alternative_is_skip) {
+                // nothing, so an immediately-following anchor is vacuous for this copy,
+                // UNLESS the skipped step carried a leading anchor of its own. In that
+                // case the adjacency transfers through the empty run to the step we skip
+                // to, so `A . Q* . B` with zero `Q` still requires `A` and `B` to be
+                // immediate siblings.
+                if (child_step->alternative_is_skip && !child_step->is_immediate) {
                   copy->skipped_quantifier = true;
                 }
               }